The present invention relates generally to precision measurements and more particularly to a zero-home locator which enables repeated measurements over long time periods to be accurately taken by defining and periodically reconfirming an inexpensive primary fiducial that is easily discerned, readily repeated and usefully related to the necessary movements of the measuring instrument or its subject.
In any precision mapping, manufacturing or measuring system, one of the most rigorous requirements for accuracy and repeatability of operation is the establishment of the primary fiducial points from which all movements and dimensionings are referenced. Once established, these points, lines or planes should be easily sensed with the degree of resolution and repeatability required for the work at hand. For example, assume that a multi-point location system is required for the precision 3D mapping of arrays of miniature elements. In such a mapping instrument, several optical axes must be aligned with several mechanical axes which must be aligned with several electronic positional readout systems. Since each axis system must retain a known positional relationship relative to the others during the time-lengthy measurement and mapping process, all moving systems must be capable of returning to a precise starting position at the start of each mapping procedure and any relative shift of the axes during mapping must be readily discernible.
These functions are performed by a zero-home locator, a device which enables a moveable member's position to be repeatedly checked with respect to its register with a fixed member.
Prior to this invention, as a rule of thumb the hardware costs of implementing zero-home into automated systems was expensive and roughly proportional to the precision required. For instance, precision to ten mils could be obtained for a few tens of dollars while precision to 0.01 mil required a few ten thousands of dollars.